This is a tube dwelling Worm Shell (Serpulorbis imbricatus) sending out a mucus net which it uses to filter food out of the water column. This feeding method is highly unusual and almost unique to this family of sea snails.
Image taken in the Lagoon Reef dive site which is part of the Small Deatched Reef system in far north Queensland in Australia.
Detached Reef's in the area are named as they are near - but not part of - the Great Barrier Reef system.